UMN Expert: Disease cases from ticks, mosquitoes, and fleas more than triple in U.S.

May 04, 2018

A CDC report out this week states that disease cases from mosquito, tick, and flea bites more than tripled in the U.S. from 2004 to 2016. And disease cases from ticks have at least doubled in Minnesota from 2004 to 2018.The CDC also identified nine new germs spread by mosquitoes and ticks that have been discovered or introduced since 2004.

Causes for this disease rise and growing public health challenge may include more global travel, reforestation, and climate change.

Of the six tick-borne diseases that can infect people in the U.S., Lyme disease is the most common. Each year, approximately 30,000 cases of Lyme disease are reported to the CDC, but it recognizes that there are about 300,000 people actually diagnosed with the disease across the U.S.

University of Minnesota School of Public Health tick expert Jonathan Oliver offers insight into what might affect vector-borne disease spread and severity; the under-reporting of Lyme disease cases; and the emergence of the longhorned tick, an East Asia species recently discovered in the U.S. for the first time.

Jonathan Oliver, PhD“It's likely that climate change will have a major impact on the distribution and severity of vector-borne diseases [those transmitted via insects], but it is difficult to predict where and how significant these changes will be. Other major factors affect the abundance and expanding range of deer ticks and may overshadow climate change in importance. These factors include changes to land use and management; increasing availability of host animals, such as white-tailed deer and white-footed mice; and shorter-term weather events, like droughts, floods, heavy snowstorms, and cold snaps.

“For decades, Lyme disease case numbers have been terribly under-reported. It is becoming clear that there are at least 10 times more cases each year than meet the official reporting criteria. In all likelihood, other tick-borne diseases are probably majorly under-reported, too.

“The longhorned tick (AKA bush tick) has been discovered on farm animals in New Jersey. This is probably the worst possible invasive tick species that could have become established in the U.S. Females can reproduce asexually and don't require male ticks to be present, so a single tick will produce rapidly exploding population numbers. This tick has a broad range of potential host animals including deer, livestock, pets, and people ensuring that hosts will be readily available. The longhorned tick can also transmit a wide variety of pathogens that can have an economic impact on livestock or a health impact on people. We don't know yet if any of these pathogens have accompanied the tick, or if the tick will become a vector of diseases already present in the U.S.”

Jonathan Oliver, PhD, is an assistant professor at the University of Minnesota School of Public Health. As a public health entomologist, he specializes in the relationship between ticks and emerging tick-borne pathogens relevant to human health.